Polyurethane elastic fiber and method for producing same

ABSTRACT

The present invention relates to polyurethane elastic fibers obtained by spinning a polyurethane resin. The polyurethane resin includes, as constituent units, a diol (a1) having a number average molecular weight of 500 to 10,000, an organic diisocyanate (b), and a chain extender (a2). The total concentration of urethane groups and urea groups in the polyurethane resin is 1.25 to 2.50 mmol/g based on the weight of the polyurethane resin. Hard segment domains of the polyurethane resin have an average domain size of 20 to 30 nm as measured with an atomic force microscope.

TECHNICAL FIELD

The present invention relates to polyurethane elastic fibers obtained byspinning a polyurethane resin, and a method of producing the same.

BACKGROUND ART

Polyurethane resins have excellent stretching properties. These resinsthus have been widely used in materials for elastomers such as paints,coating agents, sealing materials, adhesives, fiber processing agents,artificial or synthetic leathers, and rolls, and fiber products. A needexists in these applications for improvement in heat resistance ofpolyurethane resins without sacrificing their stretching properties(residual strain and elongation), in order to prevent deterioration dueto the thermal history in manufacturing or processing a final productfrom a polyurethane resin, or in order to provide a final product withimproved durability.

Non Patent Literature 1, for example, discloses a method of adjustingthe urethane group concentration and/or the urea group concentration ofa polyurethane resin in order to improve the heat resistance.

CITATION LIST Non Patent Literature

Non Patent Literature 1: Technical Information Institute Co., Ltd.,“Poriuretan no anteika rekka taisaku to mokuteki ni oujita atarashiikaishitsu gijutsu (Polyurethane Stabilization/Anti Degradation Measuresand New Modification Technologies for Specific Purposes)”, 1st edition,Sep. 29, 2004, p. 235

SUMMARY OF INVENTION Technical Problem

However, an increase in the urethane group concentration and/or the ureagroup concentration of a polyurethane resin according to the abovemethod tends to be accompanied by a decrease in the residual strain orthe elongation of the resin. This method is effective to some extent,but it fails to sufficiently improve the heat resistance and thestretching properties.

The present invention aims to provide polyurethane elastic fibers havinghigh heat resistance and excellent stretching properties (residualstrain and elongation) as well as good heat-setting properties. Thepresent invention also aims to provide a method of producing thepolyurethane elastic fibers.

Solution to Problem

The present inventors made intensive studies to solve the above problemand arrived at the present invention. The present invention relates topolyurethane elastic fibers obtained by spinning a polyurethane resin,the polyurethane resin including, as constituent units, a diol (a1)having a number average molecular weight of 500 to 10,000, an organicdiisocyanate (b), and a chain extender (a2), the total concentration ofurethane groups and urea groups in the polyurethane resin being 1.25 to2.50 mmol/g based on the weight of the polyurethane resin, hard segmentdomains of the polyurethane resin having an average domain size of 20 to30 nm as measured with an atomic force microscope. The present inventionalso relates to a method of producing the polyurethane elastic fibers,including spinning by dry spinning.

Advantageous Effects of Invention

The polyurethane elastic fibers of the present invention, obtained byspinning the polyurethane resin, have high heat resistance and excellentstretching properties as well as good heat-setting properties.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an image of hard segment domains in Example 2.

FIG. 2 is an image of hard segment domains in Comparative Example 1.

FIG. 3 is an evaluation diagram of elastic fibers in Example 1 andComparative Example 1.

DESCRIPTION OF EMBODIMENTS

A polyurethane resin as a material of the polyurethane elastic fibers ofthe present invention will be described below.

The polyurethane resin includes, as constituent units, a diol (a1)having a number average molecular weight of 500 to 10,000, an organicdiisocyanate (b), and a chain extender (a2).

Examples of the diol (a1) having a number average molecular weight of500 to 10,000 include polyoxyalkylene diols (a11), polyester diols(a12), polyetherester diols (a13), polybutadiene diols (a14), andmixtures of two or more thereof.

Examples of the polyoxyalkylene diols (a11) include compounds containinga C2-C20 dihydric alcohol with an alkylene oxide (hereinafter simply“AO”) added thereto, and mixtures of two or more thereof,

Examples of the C2-C20 dihydric alcohol include C2-C12 aliphaticdihydric alcohols [e.g., linear alcohols such as ethylene glycol(hereinafter simply “EG”), 1,3-propylene glycol, 1,4-butanediol(hereinafter simply “1,4-BG”), 1,5-pentanediol, 1,6-hexanediol,1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-dodecanediol, anddiethylene glycol (hereinafter simply “DEG”); branched alcohols such as1,2-, 1,3-or 2,3-butanediol, neopentyl glycol,2,2-diethyl-1,3-propanediol, 2-methyl-1,5-pentanediol,3-methyl-1,5-pentanediol, 2-methyl-1,6-hexanediol,3-methyl-1,6-hexanediol, 2-methyl-1,7-heptanediol,3-methyl-1,7-heptanediol, 4-methyl-1,7-heptanediol,2-methyl-1,8-octanediol, 3-methyl-1,8-octanediol, and4-methyloctanediol]; C6-C20 alicyclic dihydric alcohols [e.g.,1,4-cyclohexanediol, 1,4-bis(hydroxymethyl)cyclohexane,2,2-bis(4-hydroxycyclohexyl)propane]; and C8-C20 aromaticring-containing dihydric alcohols [e.g., m- or p-xylylene glycol,bis(hydroxyethyl)benzene, bis(hydroxyethoxy)benzene, bisphenol Aethylene oxide adducts]. The dihydric alcohols may be used alone or incombination of two or more.

Examples of the AO to be added to the dihydric alcohol include ethyleneoxide (hereinafter simply “EO”), propylene oxide (hereinafter simply“PO”), 1,2-butylene oxide, 1,3-butylene oxide, 2,3-butylene oxide,tetrahydrofuran (hereinafter simply “THF”), 3-methyltetrahydrofuran(hereinafter simply “3M-THF”), styrene oxide, α-olefin oxide, andepichlorohydrin. The AOs may be used alone or in combination of two ormore.

From the viewpoint of the tensile strength, the elongation, and theresidual strain of the polyurethane resin, it is preferred to use THFalone, EO and THF in combination, or THF and 3M-THF in combination.

If two or more AOs are used in combination, they may be bonded by randomaddition, block addition, or a combination thereof.

Specific examples of the polyoxyalkylene diols (a11) includepolyoxyethylene glycol, poly(oxy-1,2-propylene)glycol,polyoxytetramethylene glycol (hereinafter simply “PTMG”),polyoxy-3-methyltetramethylene glycol, THF/EO copolymer diol, andTHF/3M-THF copolymer diol. Among these diols (all), PTMG, THF/EOcopolymer diol, and THF/3M-THF copolymer diol are preferred from theviewpoint of the tensile strength, the elongation, and the residualstrain of the polyurethane resin.

Examples of the polyester diols (a12) include dehydrationcondensation-type polyester diols (a121), polylactone diols (a122), andpolycarbonate diols (a123).

Examples of the dehydration condensation-type polyester diols (a121)include those obtained by condensation of a low-molecular-weight diolhaving a chemical formula weight or number average molecular weight ofless than 500 with a dicarboxylic acid or an ester-forming derivativethereof [e.g., acid anhydrides, lower (C1-4) alkyl esters, acidhalides].

Examples of the low-molecular-weight diols having a chemical formulaweight or number average molecular weight of less than 500 include theabove-mentioned C2-C20 dihydric alcohols (in particular, C2-C12aliphatic dihydric alcohols), bisphenol (e.g., bisphenol A, bisphenol S,bisphenol F) AO adducts (number average molecular weight: less than500), dihydroxynaphthalene AO adducts (number average molecular weight:less than 500), and bis(2-hydroxyethyl) terephthalate.

Among these diols, C2-C12 aliphatic dihydric alcohols are preferred fromthe viewpoint of the tensile strength of the polyurethane resin. Thelow-molecular-weight diols having a chemical formula weight or numberaverage molecular weight of less than 500 may be used alone or incombination of two or more.

Examples of the dicarboxylic acids or ester-forming derivatives thereofinclude C4-C15 aliphatic dicarboxylic acids [e.g., succinic acid, adipicacid, sebacic acid, glutaric acid, azelaic acid, maleic acid, fumaricacid], C8-C12 aromatic dicarboxylic acids [e.g., terephthalic acid,isophthalic acid], and ester-forming derivatives thereof [e.g., acidanhydrides, lower alkyl esters (e.g., dimethyl ester, diethyl ester),acid halides (e.g., acids chloride)]. Preferred among these are C4-C15aliphatic dicarboxylic acids and ester-forming derivatives thereof. Thedicarboxylic acids may be used alone or in combination of two or morethereof.

Examples of the polylactone diols (a122) include those obtained byring-opening polymerization of a lactone monomer (e.g., γ-butyrolactone,γ-valerolactone, ε-caprolactone, mixtures of two or more thereof) usingany of the above C2-C20 dihydric alcohols as an initiator.

Examples of the polycarbonate diols (a123) include polycarbonate diolsobtained by condensation of one or two or more of the above C2-C12aliphatic dihydric alcohols (preferably C3-C8, more preferably C4-C6aliphatic dihydric alcohols) and a low-molecular-weight carbonatecompound (e.g., dialkyl carbonates with a C1-C6 alkyl group, alkylenecarbonates with a C2-C6 alkylene group, diaryl carbonates with a C6-C9aryl group) while performing dealcoholization.

Among the C2-C12 aliphatic dihydric alcohols usable for the preparationof the polycarbonate diol (a123), preferred linear alcohols are1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,9-nonanediol, andpreferred branched alcohols are 3-methyl-1,5-pentanediol and2-methyl-1,8-octanediol, from the viewpoint of the residual strain ofthe polyurethane resin.

Examples of the polycarbonate diols (a123) include crystallinepolycarbonate diols and amorphous polycarbonate diols. Commerciallyavailable crystalline polycarbonate diols include “DURANOL T6002”[available from Asahi Kasei Chemicals Corporation], “ETERNACOLL UH-200”[available from Ube Industries, Ltd.], “NIPPOLLAN-980R” [available fromNippon Polyurethane Industry Co., Ltd.], and “Placcel CD220” [availablefrom Daicel Corporation]. Commercially available amorphous polycarbonatediols include “PCDL G4672” [available from Asahi Kasei ChemicalsCorporation], “PCDL T5652” [available from Asahi Kasei ChemicalsCorporation], and “Kuraray Polyol C-2090” [available from Kuraray Co.,Ltd.].

Example of the polyetherester diols (a13) include those obtained bycondensation polymerization of one or more of the polyoxyalkylene diols(a11) and one or more of the dicarboxylic acids or ester-formingderivatives thereof listed above as materials of thedehydration-condensation type polyester diols.

Examples of the polybutadiene diols (a14) include those having a1,2-vinyl structure, those having 1,4-trans structure, and those havinga 1,2-vinyl structure and a 1,4-trans structure.

Other examples of the polybutadiene diols (a14) include butadienehomopolymers and butadiene copolymers (e.g., styrene-butadienecopolymers, acrylonitrile-butadiene copolymers) and hydrogenatedproducts thereof. These hydrogenated products preferably have ahydrogenation rate of 20 to 100%.

The diol (a1) having a number average molecular weight of 500 to 10,000preferably has a number average molecular weight of 500 or more,preferably 700 or more, still more preferably 1,000 or more, from theviewpoint of the elongation of the polyurethane resin. The numberaverage molecular weight of the diol (a1) having a number averagemolecular weight of 500 to 10,000 is 10,000 or less, preferably 5,000 orless, still more preferably 4,000 or less, from the viewpoint of thetensile strength of the polyurethane resin. The number average molecularweight of the diol (a1) having a number average molecular weight of 500to 10,000 in the present invention can be determined from the hydroxyvalue measured in accordance with JIS K 0070-1992 (potentiometrictitration).

In the present invention, the organic diisocyanate (b) may include anorganic diisocyanate (b1) that reacts with the diol (a1) having a numberaverage molecular weight of 500 to 10,000 and an organic diisocyanate(b2) that reacts with the chain extender (a2), described later.

The organic diisocyanates (b1) and (b2) each may be used alone or incombination of two or more. The organic diisocyanates (b1) and (b2) maybe the same as or different from each other.

Examples of the organic diisocyanate (b) usable as the organicdiisocyanate (b1) or the organic diisocyanate (b2) include C8-C26aromatic diisocyanates, C4-C22 acyclic aliphatic diisocyanates, C8-C18alicyclic diisocyanates, C10-C18 araliphatic diisocyanates, and modifiedproducts (e.g., carbodiimide-modified products, urethane-modifiedproducts, uretdione modified products) of these diisocyanates.

Specific examples of the C8-C26 aromatic diisocyanates include1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, 2,4′-diphenylmethanediisocyanate, 4,4′-diphenylmethane diisocyanate (hereinafter simply“MDI”), 4,4′-diisocyanatobiphenyl,3,3′-dimethyl-4,4′-diisocyanatobiphenyl,3,3′-dimethyl-4,4′-diisocyanatodiphenylmethane, and 1,5-naphtylenediisocyanate.

Specific examples of the C4-C22 acyclic aliphatic diisocyanates includeethylene diisocyanate, tetramethylene diisocyanate, hexamethylenediisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylenediisocyanate, lysine diisocyanate, 2,6-diisocyanatomethylcaproate,bis(2-isocyanatoethyl)carbonate, and2-isocyanatoethyl-2,6-diisocyanatohexanoate.

Specific examples of the C8-C18 alicyclic diisocyanates includeisophorone diisocyanate, dicyclohexylmethane-4,4′-diisocyanate,cyclohexylene diisocyanate, methylcyclohexylene diisocyanate,bis(2-isocyanatoethyl)-4-cyclohexylene-1,2-dicarboxylate ,2,5-norbornanediisocyanate, and 2,6-norbornane diisocyanate.

Specific examples of the C10-C18 araliphatic diisocyanates includem-xylylene diisocyanate, p-xylylene diisocyanate, andα,α,α′,α′-tetramethylxylylene diisocyanate.

Among these diisocyanates, C8-C26 aromatic diisocyanates are preferredin order to improve the tensile strength of the polyurethane resin.Specifically, MDI is particularly preferred.

Examples of the chain extender (a2) include the low-molecular-weightdiols having a chemical formula weight or number average molecularweight of less than 500 listed above as materials of the dehydrationcondensation-type polyester diols (a121), water, C2-C10 diamines (e.g.,ethylenediamine, propylenediamine, hexamethylenediamine,isophoronediamine, toluenediamine, piperazine), poly(n=2 to6)alkylene(having 2 to 6 carbon atoms)poly(n=3 to 7)amines (e.g.,diethylenetriamine, triethylenetetramine), hydrazine or derivativesthereof (e.g., dibasic acid dihydrazides such as adipic aciddihydrazide), and C2-C10 aminoalcohols (e.g., ethanolamine,diethanolamine, 2-amino-2-methylpropanol, triethanolamine).

Among these chain extenders, low-molecular-weight diols having achemical formula weight or number average molecular weight of less than500 are preferred, and C2-C12 aliphatic dihydric alcohols are morepreferred, from the viewpoint of the residual strain, the tensilestrength, and the elongation of the polyurethane resin. Specifically,ethylene glycol, diethylene glycol, 1,3-propanediol, and 1,4-butanediolare preferred. In particular, ethyleneglycol, 1,3-propanediol, and1,4-butanediol are still more preferred.

The amount of the chain extender (a2) to be used is preferably 0.1 to 10times the number of moles of the diol (a1) having a number averagemolecular weight of 500 to. 10,000 from the viewpoint of the heatresistance, the tensile strength, and the residual strain of thepolyurethane resin. The chain extenders (a2) may be used alone or incombination of two or more.

The total concentration of urethane groups and urea groups in thepolyurethane resin is 1.25 to 2.50 mmol/g based on the weight of thepolyurethane resin. If the total concentration of urethane groups andurea groups is less than 1.25 mmol/g, the tensile strength is lowered.If the total concentration of these groups is more than 2.50 mmol/g, theresidual strain is increased, and the elongation is lowered.

From the viewpoint of the residual strain of the polyurethane resin, thetotal concentration of these groups is preferably 1.55 to 2.30 mmol/g,more preferably 1.75 to 2.20 mmol/g.

The total concentration of urethane groups and urea groups in thepolyurethane resin is calculated by theoretical calculation of the totalmole ratio of the diol (a1) having a number average molecular weight of500 to 10,000 and the chain extender (a2), and the total mole ratio ofthe organic diisocyanates (b).

The hard segment domains of the polyurethane resin have an averagedomain size of 20 to 30 nm as measured with an atomic force microscope(hereinafter simply “AFM”).

If the hard segment domains have an average domain size of less than 20nm, the heat resistance is lowered.

The average domain size of the hard segment domains is preferably 21 to29 nm, more preferably 21.5 to 28.0 nm, from the viewpoint of the heatresistance, the tensile strength, and the elongation of the polyurethaneresin. The hard segment domain of the polyurethane resin herein refersto a domain that shows a phase shift of 0 to 50% as measured with anatomic force microscope. The hard segment domain is a block (B2)including the chain extender (a2) and the organic diisocyanate (b2) thatreacts with the chain extender (a2).

The term “average domain size of the hard segment domains” means theaverage size of the blocks (B2) that show a phase shift of 0 to 50% asmeasured with an AFM.

<Method of Measuring Phase Shift with AFM>

The phase shift is determined with an AFM by tapping the surface of thepolyurethane resin with a cantilever to measure the phase shift of thecantilever. A small phase shift occurs in a hard portion of the resin,whereas a large phase shift occurs in a soft portion. The results of thephase shift measurement are image-processed, whereby the hard segmentdomains, defined as above, are represented as a specific domain size.This domain size is calculated using an image-processing software.

The detection limit of this measurement method for the average domainsize of the hard segment domains is around 5 nm.

<Method of Measuring Average Domain Size of Hard Segments with AFM>

The average domain size of the hard segment domains can be measured withan AFM under the following conditions.

(Method of Preparing Sample)

The polyurethane resin is cut into a size that can be placed on thesample stage. The cut polyurethane resin is fixed on the sample stagewith double-stick tape.

(Measurement Conditions)

-   Measurement device: atomic force microscope SPI4000 Nano Navi    Station (available from SII NanoTechnology Inc.)-   Cantilever: OMCL-AC240TS-R3-   Measurement unit: E-sweep-   Scan mode: phase image

(Method of Measuring Average Domain Size)

An image obtained using an atomic force microscope is subjected to animage analysis using the following software.

-   Measurement software: WinROOF (available from Mitani Corporation)

The detection limit of this measurement method for the average domainsize of the hard segment domains is around 5 nm.

The polyurethane resin may include a block (B1) and a block (B2).

In the polyurethane resin, the block (B1) may include the diol (a1)having a number average molecular weight of 500 to 10,000 and theorganic diisocyanate (b1) that reacts with the diol (a1) having a numberaverage molecular weight of 500 to 10,000.

From the viewpoint of heat resistance, the tensile strength, and theelongation of the polyurethane resin, the block (B1) preferably has anumber average molecular weight (M_(B1)) of 4,000 to 80,000 ascalculated by Formula (1).

$\begin{matrix}{M_{B\; 1} = {\frac{{k \times M_{a\; 1}} + {r \times M_{b\; 1}}}{r - k} - {M_{b\; 1} \times 2}}} & (1)\end{matrix}$

In Formula (1), M_(a1) represents the number average molecular weight ofthe diol (a1) having a number average molecular weight of 500 to 10,000;M_(b1) represents the number average molecular weight of the organicdiisocyanate (b1); k represents the number of moles of the diol (a1)having a number average molecular weight of 500 to 10,000; and rrepresents the number of moles of the organic diisocyanate (b1).

In the polyurethane resin, the block (B2) may include the chain extender(a2) and the organic diisocyanate (b2) that reacts with the chainextender (a2).

From the viewpoint of heat resistance, the tensile strength, and theelongation of the polyurethane resin, the block (B2) preferably has anumber average molecular weight (M_(B2)) of 1,400 to 25,000 ascalculated by Formula (2).

$\begin{matrix}{M_{B\; 2} = {\frac{{i \times M_{a\; 2}} + {j \times M_{b\; 2}}}{i - j} + {M_{b\; 2} \times 2}}} & (2)\end{matrix}$

In Formula (2), M_(ae) represents the number average molecular weight ofthe chain extender (a2); M_(b2) represents the number average molecularweight of the organic diisocyanate (b2); i represents the number ofmoles of the chain extender (a2); and j represents the number of molesof the organic diisocyanate (b2).

From the viewpoint of heat resistance, the tensile strength, and theelongation of the polyurethane resin, the block (B1) more preferably hasa number average molecular weight (M_(b1)) of 4,200 to 70,000,particularly preferably 4,500 to 65,000, as calculated by Formula (1).

From the viewpoint of heat resistance, the tensile strength, and theelongation of the polyurethane resin, the block (B2) more preferably hasa number average molecular weight (M_(B2)) of 1,450 to 22,000,particularly preferably 1,475 to 20,000, as calculated by Formula (2).

The polyurethane resin preferably satisfies the following requirements(1) to (3).

(1) The ratio of the number of moles of the diol (a1) having a numberaverage molecular weight of 500 to 10,000 to the number of moles of theorganic diisocyanate (b1) that reacts with the diol (a1) having a numberaverage molecular weight of 500 to 10,000 is preferably as follows: Theratio diol (a1) having a number average molecular weight of 500 to10,000:organic diisocyanate (b1) is 1:1.05 to 1:1.5. The ratio is morepreferably 1:1.05 to 1:1.4, particularly preferably 1:1.05 to 1.3.

(2) The total number of moles of the organic diisocyanate (b1) and theorganic diisocyanate (b2) that reacts with the chain extender (a2) ispreferably 1.3 to 4.2 times, more preferably 2.0 to 3.4 times,particularly preferably 2.4 to 3.0 times the number of moles of the diol(a1) having a number average molecular weight of 500 to 10,000.

(3) The total number of moles of the diol (a1) having a number averagemolecular weight of 500 to 10,000 and the chain extender (a2) is equalto the total number of moles of the organic diisocyanate (b1) and theorganic diisocyanate (b2).

The polyurethane resin preferably has a number average molecular weightof 20,000 to 200,000, more preferably 30,000 to 190,000, particularlypreferably 40,000 to 180,000, from the viewpoint of the tensilestrength.

The number average molecular weight of the polyurethane resin can bemeasured by gel permeation chromatography under the followingconditions, for example.

-   Device: “HLC-8220GPC” (available from Tosoh Corporation)-   Column: one “Guard column α” and one “TSKgel α-M” (each available    from Tosoh Corporation]-   Sample solution: 0.125% by weight dimethylformamide solution-   Solution injection amount: 100 pL-   Flow rate: 1 mL/min-   Measurement temperature: 40° C.-   Detector: refractive index detector-   Standard: standard polystyrene

The polyurethane resin preferably has a thermal softening point of 180°C. to 280° C., more preferably 185° C. to 260° C., particularlypreferably 190° C. to 240° C., from the viewpoint of the heat resistanceof the polyurethane resin.

The thermal softening point of the polyurethane resin can be measured bythe following method.

[1] Method of Preparing Film

A solution of the polyurethane resin is applied to a release-treatedglass plate to a thickness of 1.0 mm and dried at 70° C. for three hourswith a wind-circulation dryer. Thereafter, the dried layer is peeled offfrom the glass plate to provide a film with a thickness of about 0.2 mm.

[2] Measurement Method

A specimen (length 10 mm×width 10 mm) is cut out from the film obtainedabove. In accordance with JIS K 7196, the temperature of the specimen israised from room temperature to 300° C. at 5° C./min and the thermalsoftening point is measured. TMA/SS6100 (available from SII) can be usedfor the measurement.

A method of producing the polyurethane resin as a material of thepolyurethane elastic fibers of the present invention will be describedbelow. The method of producing the polyurethane resin includes the stepof reacting an isocyanate group-containing urethane prepolymer (p), theorganic diisocyanate (b2), and the chain extender (a2), wherein theisocyanate group-containing urethane prepolymer (p) is obtained byreacting the diol (a1) having a number average molecular weight of 500to 10,000 and the organic diisocyanate (b1). This method satisfies thefollowing requirements (1) to (3).

(1) The ratio of the number of moles of the diol (a1) having a numberaverage molecular weight of 500 to 10,000 to the number of moles of theorganic diisocyanate (b1) is as follows: The ratio diol (a1) having anumber average molecular weight of 500 to 10,000:organic diisocyanate(b1) is 1:1.05 to 1:1.5.

(2) The total number of moles of the organic diisocyanate (b1) and theorganic diisocyanate (b2) is 1.3 to 4.2 times the number of moles of thediol (a1) having a number average molecular weight of 500 to 10,000.

(3) The total number of moles of the diol (a1) having a number averagemolecular weight of 500 to 10,000 and the chain extender (a2) is equalto the total number of moles of the organic diisocyanate (b1) and theorganic diisocyanate (b2).

From the viewpoint of the heat resistance and the residual strain of thepolyurethane resin, when the diol (a1) having a number average molecularweight of 500 to 10,000 is reacted with the organic diisocyanate (b1) toprepare the urethane prepolymer (p), the ratio of the number of moles ofthe hydroxy groups of the diol (a1) having a number average molecularweight of 500 to 10,000 to the number of moles of the isocyanate groupsof the organic diisocyanate (b1) is preferably as follows: The ratiohydroxy group:isocyanate group is 1:1.05 to 1:1.5. The ratio is morepreferably 1:1.05 to 1:1.4, particularly preferably 1:1.05 to 1.3.

When the diol (a1) having a number average molecular weight of 500 to10,000 is reacted with the organic diisocyanate (b1), the conditionssuch as the temperature or time may be the same as those employed inpreparation of usual urethane prepolymers.

The method of producing the polyurethane resin includes reacting theurethane prepolymer (p), the organic diisocyanate (b2), and the chainextender (a2) to prepare a polyurethane resin. The conditions such asthe temperature or time in this reaction may be the same as thoseemployed in preparation of usual urethane prepolymers. The organicdiisocyanate (b1) to be used for the preparation of the urethaneprepolymer (p) and the organic diisocyanate (b2) to be reacted with theurethane prepolymer (p) may be the same as or different from each other.

From the viewpoint of the tensile strength and the residual strain ofthe polyurethane resin, the total number of moles of the isocyanategroups of the organic diisocyanate (b1) and the isocyanate groups of theorganic diisocyanate (b2) is preferably 1.3 to 4.2 times, morepreferably 2.0 to 3.4 times, particularly preferably 2.4 to 3.0 timesthe number of moles of the hydroxy groups of the diol (a1) having anumber average molecular weight of 500 to 10,000.

From the viewpoint of the tensile strength of the polyurethane resin,the total number of moles of the hydroxy groups of the diol (a1) havinga number average molecular weight of 500 to 10,000 and the hydroxygroups of the chain extender (a2) is equal to the total number of molesof the isocyanate groups of the organic diisocyanate (b1) and theisocyanate groups of the organic diisocyanate (b2).

The polyurethane resin can be obtained by reacting the urethaneprepolymer (p), the organic diisocyanate (b2), and the chain extender(a2), as mentioned above. Preferably, an end-capping agent (a3) is addedduring the reaction of the urethane prepolymer (p), the organicdiisocyanate (b2), and the chain extender (a2) so as to terminate theextending reaction by capping the ends of the polymer.

Examples of the end-capping agent (a3) include C1-C18 monoalcohols (a31)and C2-C20 monoamines (a32). The end-capping agents (a3) may be usedalone or in combination of two or more.

Examples of the C1-C18 monoalcohols (a31) include linear monools (e.g.,methanol, ethanol, n-propanol, n-butanol, pentanol, hexanol, octanol,nonyl alcohol, decyl alcohol, undecyl alcohol, dodecyl alcohol, tridecylalcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol);branched chain-containing monools (e.g., isopropanol, sec-, iso- ortert-butanol, neopentyl alcohol, 3-methyl-pentanol, 2-ethylhexanol);C6-C10 cyclic group-containing monools [e.g., alicyclic group-containingmonools (e.g., cyclohexanol) and aromatic ring-containing monools (e.g.,benzyl alcohol)]; polymer monools (e.g., polyester monool, polyethermonool, polyetherester monool); cellosolves; carbitols; and mixtures oftwo or more thereof.

Among these monoalcohols, linear monools are preferred. Specifically,methanol, ethanol, n-propanol, n-butanol, and the like are preferred.

Examples of the C2-C20 monoamines (a32) include mono- or dialkylaminescontaining a C1-C8 alkyl group such as ethylamine, n-propylamine,isopropylamine, n-butylamine, diethylamine, di-n-propylamine,diisopropylamine, and di-n-butylamine; C6-C10 alicyclic monoamine suchas cyclohexylamine; C6-C10 aromatic monoamines such as aniline; mono- ordialkanolamines containing C2-C4 alkanol group such as monoethanolamine,monoisopropanolamine, diethanolamine, diisopropanolamine; heterocyclicmonoamines such as morpholine; and mixtures of two or more thereof.

For the termination of the extending reaction by capping the ends of thepolymer, the end-capping agent (a3) is preferably added when the weightproportion of isocyanate groups reaches 0.01 to 0.3% by weight in thereaction mixture containing the urethane prepolymer (p), the organicdiisocyanate (b2), and the chain extender (a2). More preferably, theend-capping agent (a3) is added when the weight proportion of theisocyanate groups reaches 0.03 to 0.13% by weight.

If an organic solvent or an additive (described later) is used in thepreparation of the polyurethane resin, it is difficult to directlydetermine the weight proportion of the isocyanate groups in the reactionmixture containing the urethane prepolymer (p), the organic diisocyanate(b2), and the chain extender (a2). In this case, the ratio of the totalamount of the urethane prepolymer (p), the organic diisocyanate (b2),and the chain extender (a2) to the total amount of the reaction mixtureis multiplied by the above-mentioned weight proportion range ofisocyanate groups, so as to determine a target range of the weightproportion of isocyanate groups for the addition of the end-cappingagent (a3). The end-capping agent (a3) is added when the measured valueof the isocyanate group-content of the reaction mixture containing anorganic solvent and other components reaches the target range.

The conditions in the termination of the extending reaction such astemperature or time may be the same as those employed in the terminationof the extending reaction in preparation of a usual polyurethane resin.

In the method of producing the polyurethane resin; an organic solventmay be used in any production steps. Any organic solvent may be used.Examples thereof include C3-C10 ketone solvents (e.g., acetone, methylethyl ketone, methyl isobutyl ketone), C2-C10 ester solvents (e.g.,ethyl acetate, butyl acetate, y-butyrolactone), C4-C10 ether solvents(e.g., tetrahydrofuran, diethylene glycol dimethyl ether), C3-C10 amidesolvents [e.g., N,N-dimethylformamide, N,N-dimethylacetamide(hereinafter simply “DMAC”), N-methyl-2-pyrolidone,N-methylcaprolactam], C2-C10 sulfoxide solvents (e.g., dimethylsulfoxide), C1-C8 alcohol solvents (e.g., methanol, ethanol, isopropylalcohol, octanol), and C4-C10 hydrocarbon solvents (e.g., n-butane,cyclohexane, toluene, xylene).

Among these organic solvents, C3-C10 amide solvents and C2-C10 sulfoxidesolvents are preferred, and C3-C10 amide solvents are more preferred,from the viewpoint of the solubility of the polyurethane resin.Specifically, N,N-dimethylformamide and DMAC are more preferred.

If an organic solvent is used, the amount thereof is preferably suchthat the concentration of the polyurethane resin to be obtained is 10 to90% by weight, more preferably 20 to 80% by weight.

In the preparation of the polyurethane resin, a catalyst that is usuallyused in production of a polyurethane resin may be optionally used inorder to promote the reaction. Specific examples of the catalyst includeorganic metal compounds [e.g., dibutyltin dilaurate, dioctyltin laurate,bismuth carboxylate, bismuth alkoxides, chelate compounds formed fromdicarbonyl group-containing compounds and bismuth], inorganic metalcompounds [e.g., bismuth oxide, bismuth hydroxide, bismuth halides],amines [e.g., triethylamine, triethylenediamine, diazabicycloundecene],and any combination of two or more thereof.

Furthermore, a pigment, a stabilizer, and other additives (e.g., afusion inhibitor, a flame retardant) may be added in any step in themethod of producing the polyurethane resin. The polyurethane resincomposition thus produced using an additive is a polyurethane resincomposition containing the polyurethane resin and an additive.

The present invention also encompasses polyurethane elastic fibersobtained by spinning such a polyurethane resin composition containingthe polyurethane resin and an additive.

Any pigment may be used. An organic pigment and/or an inorganic pigmentknown in the art may be used. The amount of the pigment to be used isusually 0 to 5% by weight, preferably 0.1 to 3% by weight based on theweight of the polyurethane resin to be obtained. Examples of the organicpigment include insoluble azo pigments, soluble azo pigments, copperphthalocyanine pigments, and quinacridone pigments. Examples of theinorganic pigment include chromates, ferrocyanides, metal oxides,selenium sulfide compounds, metal salts (e.g., sulfates, silicates,carbonates, phosphates), metal powder, and carbon black.

Any stabilizer may be used. An antioxidant and/or an ultravioletabsorber known in the art may be used. The amount of the stabilizer tobe used is usually 0 to 5% by weight, preferably 0.1 to 3% by weightbased on the weight of the polyurethane resin to be obtained.

Examples of the antioxidant include phenolic antioxidants [e.g.,2,6-di-t-butyl-p-cresol, butylated hydroxyanisole]; bisphenolicantioxidants [e.g., 2,2′-methylenebis(4-methyl-6-t-butylphenol)]; andphosphoric antioxidants [e.g., triphenylphosphite,diphenylisodecylphosphite].

Examples of ultraviolet absorbers include benzophenone ultravioletabsorbers [e.g., 2,4-dihydroxybenzophenone,2-hydroxy-4-methoxybenzophenone];

benzotriazole ultraviolet absorbers [e.g.,2-(2′-hydroxy-5′-methylphenyl)benzotriazole]; salicylic acid ultravioletabsorbers [e.g., phenyl salicylate]; and hindered amine ultravioletabsorbers [e.g., bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate].

The above polyurethane resin and the above polyurethane resincomposition have high heat resistance and are excellent in stretchingphysical properties such as the tensile strength and the elongation. Byspinning the polyurethane resin and/or the polyurethane resincomposition, the polyurethane elastic fibers of the present inventioncan be obtained.

If the polyurethane resin or the polyurethane resin composition is spuninto the polyurethane elastic fibers of the present invention by meltspinning, the resin or the resin composition is used in a molten form,in a solvent-free pellet from, or in a solvent-free block form. If thepolyurethane resin or the polyurethane resin composition is spun by dryspinning, the resin or the resin composition is used in the form of apolyurethane resin solution that usually has a resin concentration of 30to 80% by weight. The solution is prepared by dilution with any of theabove-mentioned solvents, such as DMCA.

The polyurethane elastic fibers obtained by spinning the polyurethaneresin or the polyurethane resin composition can be obtained by, forexample, dry spinning, wet spinning, or melt spinning using the abovepolyurethane resin solution as a spinning dope, and winding theresulting fibers. In particular, dry spinning is preferred becauseelastic fibers obtained by dry spinning can have large hard segmentdomain crystals, so that they can exhibit high breaking elongation, highthermal softening point, excellent chemical resistance, low coefficientof variation of the fineness, and also because fibers of any finenesscan be stably spun.

The polyurethane elastic fibers of the present invention obtained byspinning the polyurethane resin or the polyurethane resin compositionmay have any fineness or any cross-sectional shape. For example, thepolyurethane elastic fibers of the present invention may have a circularcross-sectional shape or a flat cross-sectional shape.

The dry spinning method is not limited. Spinning conditions areappropriately selected according to desired characteristics or spinningequipment.

For example, the permanent strain and the stress relaxation ofpolyurethane elastic fibers are preferably appropriately determinedaccording to the applications of the elastic fibers, because theseproperties are especially susceptible to the speed ratio of a godetroller to a winder. In order to obtain polyurethane elastic fibers withdesired permanent strain and stress relaxation, winding is preferablyperformed at a speed ratio of a godet roller to a winder of 1.10 or morebut 1.65 or less. In particular, in order to obtain polyurethane elasticfibers with high permanent strain and low stress relaxation, the speedratio of a godet roller to a winder is more preferably 1.15 or more but1.4 or less, still more preferably 1.15 or more but 1.35 or less.

In order to obtain polyurethane elastic fibers with low permanent strainand high stress relaxation, winding is preferably performed at a speedratio of a godet roller to a winder of 1.25 or more but 1.65 or less,more preferably 1.35 or more but 1.65 or less.

The spinning rate is preferably 450 m/min or more in order to improvethe strength of the polyurethane elastic fibers to be obtained.

The polyurethane elastic fibers of the present invention obtained in theabove-described manner are used to produce a fabric, for example, incombination with other fibers. Examples of other fibers to be used withthe polyurethane elastic fibers for fabric production include polyamidefibers and polyester fibers.

Such other fibers to be used in combination with the polyurethaneelastic fibers of the present invention are preferably filaments inorder to produce a fabric with good appearance reflecting the highheat-setting properties and the low coefficient of variation of thefineness of the polyurethane elastic fibers of the present invention.

The polyamide fibers are fibers exemplified by, but not limited to,nylon 6 fibers or nylon 66 fibers. The polyester fibers are fibers madeof polyesters. Examples of the polyesters include polyethyleneterephthalate, polytrimethylene terephthalate, polytetramethyleneterephthalate, ester copolymers mainly consisting of polytetramethyleneglycol and ethylene glycol as diol components, and cationic-dyeablepolyesters obtained by modifying these polyesters.

A fabric made from the polyurethane elastic fibers of the presentinvention obtained by spinning the polyurethane resin or thepolyurethane resin composition preferably contains the above polyamidefibers or the above polyester fibers, from the viewpoint of theprocessability and the durability of the fabric. The fabric may containsynthetic fibers such as polyacrylic fibers and polyvinyl chloridefibers, regenerated cellulose fibers such as cuprammonium rayon, viscoserayon, and purified cellulose, regenerated protein fibers, semisyntheticfibers, and natural fiber materials such as cotton, silk, and wool.

The polyurethane elastic fibers in the fabric may be in the form of abare yarn or in the form of a conjugated yarn, such as a core spun yarnin which the polyurethane elastic fibers are covered with other fibers,an air covered yarn in which the polyurethane elastic fibers are coveredwith other fibers, a plied yarn with other fibers, a twisted union yarnwith other fibers, and an interlaced yarn with other fibers. The fabriccontaining the polyurethane elastic fibers and other fibers may be aknitted fabric containing any of the above conjugated yarns.Alternatively, the fabric may be produced by knitting the polyurethaneelastic fibers in combination with other fibers by warp knitting,circular knitting, weft knitting, or the like.

If the fabric is a knitted fabric, it may be a warp knitted fabric or aweft knitted fabric. Examples thereof include tricot, raschel, andcircular knitted fabrics. The knitting structure may be any knittingstructure, such as half stitch, back half stitch, double atlas stitch,or double denbigh stitch. From the viewpoint of the texture, the surfaceof the knitted fabric preferably contains natural fibers, chemicalfibers, or synthetic fibers other than polyurethane elastic fibers.

EXAMPLES

The present invention will be further described with reference toexamples. The present invention is not limited to the examples.

Examples 1 to 9 and Comparative Examples 3 and 4

In accordance with the formulation shown in Table 1, a reactioncontainer equipped with a stirring device and a temperature controldevice was charged with a diol (a1) having a number average molecularweight of 500 to 10,000, an organic diisocyanate (b1), and an organicsolvent. These compounds were reacted under a nitrogen atmosphere at 70°C. for seven hours. Thus, a urethane prepolymer (p) was obtained.Subsequently, a chain extender (a2) and an organic diisocyanate (b2)were added to the reaction container. These compounds were reacted undera nitrogen atmosphere at 70° C. When the weight proportion of isocyanategroups in the reaction mixture reached the value shown in Table 2 or 3,an end-capping agent (a3) was added to the reaction mixture so as toterminate the extending reaction by capping the ends of the polymer. Thecapping reaction was performed for one hour. In this manner,polyurethane resin solutions (P-1) to (P-9) of Example 1 to 9 andpolyurethane resin solutions (R-3) and (R-4) of Comparative Examples 3and 4 were obtained.

Comparative Examples 1 and 2

In accordance with the formulation shown in Table 1, a reactioncontainer equipped with a stirring device and a temperature controldevice was charged with a diol (a1) having a number average molecularweight of 500 to 10,000, a chain extender (a2), organic diisocyanates(b1) and (b2) (Table 1 shows the total amount of diisocyanates added.)and an organic solvent. These compounds were reacted under a drynitrogen atmosphere at 70° C. When the weight proportion of isocyanategroups in the reaction mixture reached the value shown in Table 3, anend-capping agent (a3) was added to the reaction mixture so as toterminate the extending reaction by capping the ends of the polymer. Thecapping reaction was performed for one hour. In this manner,polyurethane resin solutions (R-1) and (R-2) of Comparative Examples 1and 2 were obtained.

The diols (a1) having a number average molecular weight of 500 to 10,000listed in Table 1 have the following compositions.

PTMG1500: polyoxytetramethylene glycol having a number average molecularweight of 1,500 [“PTMG1500”, available from Mitsubishi ChemicalCorporation]

PTMG2000: polyoxytetramethylene glycol having a number average molecularweight of 2,000 [“PTMG2000”, available from Mitsubishi ChemicalCorporation]

PTMG3000: polyoxytetramethylene glycol having a number average molecularweight of 3,000 [“PTMG3000”, available from Mitsubishi ChemicalCorporation]

THF/EO copolymer: tetrahydrofuran/ethylene oxide copolymer diol having anumber average molecular weight of 2,000 and a mole ratio of THF to EOof 70:30

THF/3M-THF copolymer: tetrahydrofuran/3-methyltetrahydrofuran copolymerdiol having a number average molecular weight of 2,000 [“PTGL2000”,available from Hodogaya Chemical Co., Ltd.]

SANESTOR 24625: dehydration condensation-type polyester diol having anumber average molecular weight of 2,500 [“SANESTOR 24625”, availablefrom Sanyo Chemical Industries, Ltd.]

TABLE 1 Example Comparative Example 1 2 3 4 5 6 7 8 9 1 2 3 4Polyurethane resin solution (P-1) (P-2) (P-3) (P-4) (P-5) (P-6) (P-7)(P-8) (P-9) (R-1) (R-2) (R-3) (R-4) Constituent Diol (a1) Polyoxy-PTMG1500 — — — — — 214 — — — — — — — unit having alkylene PTMG2000 213213 213 213 — — — — — 216 190 213 170 (parts by a number diol (a11)PTMG3000 — — — — 211 — — — — — — — — weight) average THF/EO — — — — — —213 — — — — — — molecular copolymer weight of THF/3M-THF — — — — — — —213 — — — — — 500 to copolymer 10000 Polyester SANESTOR — — — — — — — —212 — — — — diol (a12) 24625 Chain extender (a2) Ethylene 12 12 12 12 149 12 12 13 12 18 12 21 glycol End-capping agent n-Butanol 5 5 5 5 3 6 55 4 4 4 5 4 (a3) Organic diisocyanate MDI 28 32 35 40 19 38 28 28 22 7494 45 22 (b1) Organic diisocyanate MDI 45 41 38 33 55 35 45 45 51 28 84(b2) Organic solvent DMAC 698 698 698 698 699 698 698 698 699 693 695698 699 Total (parts by weight) 1000 1000 1000 1000 1000 1000 1000 10001000 1000 1000 1000 1000

With the polyurethane resin solutions obtained in Examples 1 to 9 andComparative Examples 1 to 4, the tensile strength at break, theelongation at break, the residual strain, and the thermal softeningpoint were measured by the following methods. The results are shown inTable 2.

[1] Method of Preparing Film

The polyurethane resin solution was applied to a release-treated glassplate to a thickness of 1.0 mm and dried at 70° C. for three hours witha wind-circulation dryer. Thereafter, the dried resin was peeled offfrom the glass plate. Thus, a film with a thickness of about 0.2 mm wasprepared.

[2] Method of Measuring Strength and Elongation of Film

The film obtained above was allowed to stand for one hour in a room witha controlled temperature of 25° C. and a controlled humidity of 65% RH.Thereafter, the tensile strength at break and the elongation at breakwere measured in accordance with JIS K 6251. The greater these valuesare, the better the elastic fiber performance is. The parallel portionof the dumbbell specimen was 200 μm in thickness and 5 mm in width. Theinitial gauge length was 20 mm.

[3] Method of Measuring Residual Strain

A strip-shaped specimen (length 100 mm×width 5 mm) was cut out of thefilm obtained above. The specimen was marked with bench marks such thatthe gauge length was 50 mm. This specimen was set in the chucks of anInstron tensile tester (autograph, available from Shimadzu Corp.). Thespecimen was stretched at a 25° C. atmosphere at a constant rate of 500mm/min until the gauge length reached 300%, and then the specimen wasallowed to return at the same rate so that the inter-chuck distancereached its value before the stretching.

The gauge length (D1) after this operation was measured. The residualstrain (%) was determined by the following formula using the value (D1)and the gauge length before the test (D0=50 mm).

Residual strain (%)={(D1-D0)/D0}×100

[4] Measurement of Thermal Softening Point

A strip-shaped specimen (length 100 mm×width 5 mm) was cut out of thefilm obtained above. In accordance with JIS K 7196, the temperature ofthe specimen was raised from room temperature to 300° C. at 5° C./rainand the thermal softening point was measured. TMA/SS6100 (available fromSII) was used for the measurement.

The higher the thermal softening point is, the better heat resistancethe polyurethane resin has.

[5] Method of Measuring Average Domain Size of Hard Segment Domains withAFM

(Method of Preparing Sample)

The polyurethane resin was cut to a size that could be placed on thesample stage. The cut polyurethane resin was fixed to the sample stagewith double-stick tape.

(Measurement Conditions)

-   Device: atomic force microscope SPI4000 Nano Navi Station (available    from SII NanoTechnology Inc.)-   Cantilever: OMCL-AC240TS-R3-   Measurement unit: E-sweep-   Scan mode: phase image

(Method of Measuring Average Domain Size)

An image measured with an atomic force microscope was subjected to imageanalysis using the following software.

-   Measurement software: WinROOF (available from Mitani Corporation)

FIGS. 1 and 2 are images of hard segment domains in Examples 2 andComparative Example 1.

FIG. 1 is an image of hard segment domains in Example 2.

A gray scale bar in the lower part of FIG. 1 shows the degree of thephase shift of the cantilever. The left half of the bar, i.e., the darkportion, corresponds to a phase shift of 0 to 50%. Domains displayed inthe dark color are hard segment domains in Example 2.

FIG. 2 is an image of hard segment domains in Comparative Example 1. Theinterpretation of FIG. 2 is the same as that of FIG. 1.

Table 2 shows the average domain size of the hard segment domains, theurethane group concentration and the urea group concentration of thepolyurethane resin, the number average molecular weight of the block(B1), the number average molecular weight of the block (B2), and thenumber average molecular weight of the polyurethane resin.

[6] Method of Calculating Urethane Group Concentration and Urea GroupConcentration

These concentrations were calculated by theoretical calculation of thetotal mole ratio of the diol (a1) having a number average molecularweight of 500 to 10,000 and the chain extender (a2) and the total moleratio of the organic diisocyanates (b).

Table 2 shows the total concentration of urethane groups and ureagroups.

[7] Method of Calculating Number Average Molecular Weight of Blocks (B1)and (B2)

The number average molecular weight (M_(B1)) was calculated by Formula(1) based on the block (B1) including the diol (a1) having a numberaverage molecular weight of 500 to 10,000 and the organic diisocyanate(b1) that reacts with the diol (a1) having a number average molecularweight of 500 to 10,000.

$\begin{matrix}{M_{B\; 1} = {\frac{{k \times M_{a\; 1}} + {r \times M_{b\; 1}}}{r - k} - {M_{b\; 1} \times 2}}} & (1)\end{matrix}$

In Formula (1), M_(a1) represents the number average molecular weight ofthe diol (a1) having a number average molecular weight of 500 to 10,000;M_(b1) represents the number average molecular weight of the organicdiisocyanate (b1); k represents the number of moles of the diol (a1)having a number average molecular weight of 500 to 10,000; and rrepresents the number of moles of the organic diisocyanate (b1).

The number average molecular weight (M_(B2)) was calculated by Formula(2) based on the block (B2) including the chain extender (a2) and theorganic diisocyanate (b2) that reacts with the chain extender (a2).

$\begin{matrix}{M_{B\; 2} = {\frac{{i \times M_{a\; 2}} + {j \times M_{b\; 2}}}{i - j} + {M_{b\; 2} \times 2}}} & (2)\end{matrix}$

In Formula (2), M_(a2) represents the number average molecular weight ofthe chain extender (a2); M_(b2) represents the number average molecularweight of the organic diisocyanate (b2); i represents the number ofmoles of the chain extender (a2), and j represents the number of molesof the organic diisocyanate (b2).

Table 2 shows the number average molecular weight of the block (B1) andthe number average molecular weight of the block (B2).

[8] Method of Measuring Number Average Molecular Weight of PolyurethaneResin

The number average molecular weight of the polyurethane resin wasmeasured by gel permeation chromatography under the followingconditions.

-   Device: “HLC-8220GPC” (available from Tosoh Corporation)-   Column: one “Guard column a” and one “TSKgel a-M” (each available    from Tosoh Corporation-   Sample solution: 0.125% by weight dimethylformamide solution-   Solution injection amount: 100 μL-   Flow rate: 1 mL/min-   Measurement temperature: 40° C.-   Detector: refractive index detector-   Standard: standard polystyrene

Table 2 shows the number average molecular weight of the polyurethaneresin.

Polyurethane elastic fibers (L-1) to (L-9) and (L′-1) to (L′-4) wereprepared by the method below using the polyurethane resin solutionsobtained in Examples 1 to 9 and Comparative Examples 1 to 4. Thebreaking elongation, the breaking strength, the permanent strain, thestress relaxation, the thermal softening point, the heat setting, thechemical resistance, and the coefficient of variation of the fineness ofthe polyurethane elastic fibers were measured. The results are shown inTable 3.

[9] Method of Preparing Polyurethane Elastic Fibers (L-1) to (L-9) and(L′-1) to (L′-4)

Polyurethane disclosed in U.S. Pat. No. 3,555,115, prepared by reactingt-butyldiethanolamine and methylene-bis-(4-cyclohexylisocyanate), wasmixed with a condensation polymer of p-cresol and divinylbenzenedisclosed in U.S. Pat. No. 3,553,290 at a weight ratio of 2:1. Asolution (35% by weight) of the mixture in DMAC was prepared to be usedas an antioxidant solution (35% by weight). Each of the polyurethaneresin solutions [(P-1) to (P-9) and (R-1) to (R-4)] obtained in Examples1 to 9 and Comparative Examples 1 to 4 (97% by weight) and theantioxidant solution (3% by weight) were uniformly mixed to prepare asolution. This solution was subjected to dry spinning at 490 m/min and aspeed ratio of a godet roller to a winder of 1.4. Thus, 300 g of woundpolyurethane elastic fibers (33 dtex, 3 filaments) were obtained.

[10] Breaking Elongation, Breaking Strength, Stress Relaxation, andPermanent Strain of Polyurethane Elastic Fibers

The breaking strength, the stress relaxation, the permanent strain, andthe breaking elongation were measured by subjecting a sample yarn to atensile test using an Instron 4502 tensile tester.

These properties are defined as follows. A sample (5 cm (L1)) wasstretched 300% at a pulling speed of 50 cm/min five times. The stress atthe fifth stretch is taken as (G1).

Subsequently, 300% stretch was held for 30 seconds. The stress after the30-second holding is taken as (G2). Then, the sample was allowed torecover from the stretch. The length of the sample yarn when the stressreached 0 is taken as (L2). Thereafter, the sample yarn was stretchedfor the sixth time until the yarn broke. The stress at break is taken as(G3), and the length of the sample yarn at break is taken as (L3).

The above properties are determined in accordance with the followingformulae.

Breaking strength=(G3)

Stress relaxation=100×((G1)−(G2))/(G1)

Permanent strain=100−((L2)−(L1))/(L1)

Breaking elongation=100×((L3)−(L1))/(L1)

[11] Thermal Softening Point of Polyurethane Elastic Fibers

The temperature dispersion of the dynamic storage elastic modulus E′ wasmeasured at a rate of temperature increase of 10° C./rain using adynamic elastic modulus analyzer RSA II, available from RheometricScientific, Inc. The thermal softening point was determined from theintersection point at which the tangent on the E′ curve in the plateauregion from 80° C. to 130° C. intersects the tangent on the E′ curve inthe region where E′ drops owing to thermal softening at 160° C. orhigher. E′ is plotted on the logarithmic axis, and the temperature onthe linear axis.

FIG. 3 is an evaluation diagram of elastic fibers, showing measurementcurves of the thermal softening point of the elastic fibers in Example 1and Comparative Example 1.

[12] Heat-Setting Properties of Polyurethane Elastic Fibers

A sample yarn (length=L5) was stretched 100% (length=2 ×(L5)). While thelength was held, the yarn was heat-treated at 160° C. for one minute.The yarn was further allowed to stand at room temperature for one daywhile the same length was held. Thereafter, the sample yarn was releasedfrom the stretch, and the length (L6) of the yarn was measured.

Heat-setting properties=100×((L6)-(L5))/(L5)

The higher this value is, the better the heat-setting properties are.

[13] Chemical Resistance of Polyurethane Elastic Fibers

A yarn was held at a 100% stretch state and subjected to the followingthree exposure treatments. First, the yarn was immersed in a solution ofoleic acid (5% by weight) in hexane for one hour. Next, a hypochlorousacid solution (chlorine concentration: 500 ppm) was prepared, and theyarn was immersed therein for two hours. Then, the yarn was exposed toUV for two hours. The UV exposure treatment was performed using a carbonarc-type fade meter, available from Suga Test Instruments Co., Ltd., at63° C. and 60% RH. This exposure treatment was performed twice.Thereafter, the yarn was allowed to stand in a state free fromtreatments for 24 hours at room temperature. The breaking strength (G4)was measured in the same manner as described above. The ratio(retention) of the breaking strength (G4) of the treated yarn to thebreaking strength (G3) of an untreated yarn is taken as the chemicalresistance.

Chemical resistance (%)=100−(G4)/(G3)

[14] Coefficient of Variation of Fineness of Polyurethane Elastic Fibers

On the surface of the package of the wound polyurethane elastic fibers,the first 50 m of the polyurethane elastic fibers were removed toeliminate inaccuracy due to handling damage. Then, polyurethane elasticfibers were drawn from the package for 130 seconds using a rollingtake-off unit, and passed through a tensiometer equipped with apiezoceramic pin. The circumference of the take-up roll was 50% greaterthan that of the feed roll, and these rolls rotated at the same speed.As a result, the polyurethane elastic fibers were elongated 50% whenthey pass through the tensiometer. The tension when the polyurethaneelastic fibers were fed through the roll was measured with thetensiometer. Since the fineness of the fibers is directly proportionalto the tension, the coefficient of variation was obtained by dividingthe standard deviation of the tension by the average tension. Thecoefficient of variation of the fineness is independent of the finenessof the fibers. A small coefficient of variation of the fineness of thefibers indicates high fiber uniformity.

[15] A Stretch Woven Fabric was Prepared in the Following Manner. TheAppearance of the Fabric was Evaluated.

The obtained polyurethane elastic fibers were subjected to coveringprocessing. A nylon filament 168 dtex-24 fil was used as a coveringyarn. A covered yarn for weft was prepared with a covering machine at anumber of twists of 450 t/m and a draft of 3.0. Similarly, a coveredyarn for warp was prepared with a covering machine using the same nylonfilament covering yarn at a number of twists of 700 t/m and a draft of3.5.

Subsequently, the covered yarns were warped and weaved. Specifically,5100 warp yarns (beam warping 1100 yarns) were sized and warped, andthen the yarns were woven into a 2/1 twill using a Rapier loom.

Thereafter, the fabric was dyed. The gray fabric obtained by the weavingwas subjected to, sequentially, refinement, intermediate setting (175°C.), embossment (180° C.), dyeing (98° C.), drying, a finishing-agenttreatment, and finishing setting (175° C., cloth-feeding speed: 20m/min, setting zone: 24 m) by usual methods.

The appearance was visually evaluated in accordance with the followingcriteria.

∘: No defects were observed in the stretch woven fabric. Δ: Streaks inthe warp direction were observed on the stretch woven fabric. ×: Yarnsfrequently broke during the preparation of the covered yarns.

TABLE 2 Example 1 2 3 4 5 Polyurethane resin solution (P-1) (P-2) (P-3)(P-4) (P-5) Production Number of moles of hydroxy groups of (a1): 1:1.051:1.2 1:1.3 1:1.5 1:1.05 conditions number of moles of isocyanatesgroups of (b1) [Total number of moles of isocyanates of (b1) 2.7 2.7 2.72.7 4.2 and (b2)]/number of moles of hydroxy groups of (a1) Relationbetween total number of moles of Equal Equal Equal Equal Equalisocyanate groups of (b1) and (b2) and total number of moles of hydroxygroups of (a1) and (a2) Weight proportion (%) of isocyanate groups in0.011 0.012 0.012 0.011 0.011 reaction mixture when (a3) is addedProduction method Prepolymer Prepolymer Prepolymer Prepolymer Prepolymermethod method method method method Polyurethane Total concentration ofurethane groups and 1.93 1.93 1.93 1.93 1.94 resin urea groupscomposition (mmol/g) Mverage domain size (nm) of 23.3 22.6 22.3 22.124.0 hard segment domains Number average molecular weight (M_(B1)) of44,750 11,000 7,250 4,250 64,750 block (B1) MNumber average molecularweight (M_(B2)) of 11,046 3,090 2,206 1,499 20,406 block (B2) Numberaverage molecular weight of 53,000 56,000 61,000 62,000 57,000polyurethane resin Evaluation Tensile strength at break (MPa) 67 68 7172 68 results Elongation at break (%) 700 700 700 700 680 Residualstrain (%) 30 31 31 32 31 Thermal softening point (° C.) 230 226 222 220236 Example 6 7 8 9 Polyurethane resin solution (P-6) (P-7) (P-8) (P-9)Production Number of moles of hydroxy groups of (a1): 1:1.05 1:1.051:1.05 1:1.05 conditions number of moles of isocyanates groups of (b1)[Total number of moles of isocyanates of (b1) 2.0 2.7 2.7 3.4 and(b2)]/number of moles of hydroxy groups of (a1) Relation between totalnumber of moles of Equal Equal Equal Equal isocyanate groups of (b1) and(b2) and total number of moles of hydroxy groups of (a1) and (a2) Weightproportion (%) of isocyanate groups in 0.011 0.012 0.012 0.011 reactionmixture when (a3) is added Production method Prepolymer PrepolymerPrepolymer Prepolymer method method method method Polyurethane Totalconcentration of urethane groups and 1.92 1.93 1.93 1.94 resin ureagroups composition (mmol/g) Mverage domain size (nm) of 23.1 23.2 23.323.3 hard segment domains Number average molecular weight (M_(B1)) of34,750 44,750 44,750 44,750 block (B1) MNumber average molecular weight(M_(B2)) of 6,678 11,046 11,046 15,414 block (B2) Number averagemolecular weight of 49,000 45,000 53,000 65,000 polyurethane resinEvaluation Tensile strength at break (MPa) 66 65 67 75 resultsElongation at break (%) 700 720 700 680 Residual strain (%) 34 31 31 34Thermal softening point (° C.) 228 230 230 231 Comparative Example 1 2 34 Polyurethane resin solution (R-1) (R-2) (R-3) (R-4) Production Numberof moles of hydroxy groups of (a1): — — 1:1.7 1:1.05 conditions numberof moles of isocyanates groups of (b1) [Total number of moles ofisocyanates of (b1) 2.7 4.0 2.7 5.0 and (b2)]/number of moles of hydroxygroups of (a1) Relation between total number of moles of Equal EqualEqual Equal isocyanate groups of (b1) and (b2) and total number of molesof hydroxy groups of (a1) and (a2) Weight proportion (%) of isocyanategroups in 0.011 0.012 0.011 0.012 reaction mixture when (a3) is addedProduction method One-shot One-shot Prepolymer Prepolymer method methodmethod method Polyurethane Total concentration of urethane groups and1.93 2.47 1.93 2.82 resin urea groups composition (mmol/g) Mveragedomain size (nm) of 18.6 18.8 18.7 23.3 hard segment domains Numberaverage molecular weight (M_(B1)) of — — 2,964 44,750 block (B1) MNumberaverage molecular weight (M_(B2)) of — — 1,214 25,398 block (B2) Numberaverage molecular weight of 57,000 64,000 55,000 60,000 polyurethaneresin Evaluation Tensile strength at break (MPa) 68 78 67 90 resultsElongation at break (%) 700 550 700 500 Residual strain (%) 38 50 37 60Thermal softening point (° C.) 205 215 206 235

TABLE 3 Example Comparative Example 1 2 3 4 5 6 7 8 9 1 2 3 4Polyurethane elastic fiber (L-1) (L-2) (L-3) (L-4) (L-5) (L-6) (L-7)(L-8) (L-9) (L′-1) (L′-2) (L′-3) (L′-4) Elastic Breaking elongation (%)480 470 470 465 455 480 485 470 460 395 340 405 360 fiber Breakingstrength (cN) 28 29 29 27 27 30 26 28 30 25 36 24 38 evaluationPermanent strain (%) 19 20 20 20 22 20 19 20 20 27 38 25 43 resultsStress relaxation (%) 30 31 33 33 34 31 32 31 32 34 42 32 47 Thermalsoftening point (° C.) 198 199 195 195 206 198 200 201 204 182 185 182188 Heat setting (%) 53 52 55 56 51 52 52 51 53 52 48 52 44 Chemicalresistance (%) 83 77 75 75 87 80 82 80 84 33 42 38 51 Coefficient ofvariation of 8.1 8.9 8 9.3 7.9 8.8 8.3 8.1 8.5 28.6 22.2 21.7 23.4fineness (—) Appearance evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Δ Δ Δ X

The films (urethane sheets) obtained from the polyurethane resinsolutions of Examples 1 to 9 had high heat resistance and excellentstretching properties. The films (urethane sheets) obtained from thepolyurethane resin solutions of Comparative Examples 1 to 3 had a lowthermal softening point. The film (urethane sheet) obtained from thepolyurethane resin solution of Comparative Example 4 had poor stretchingproperties.

The stretch woven fabrics obtained from the polyurethane elastic fibersof Examples 1 to 9 had no defects and had excellent appearance. Thestretch woven fabrics obtained from the polyurethane elastic fibers ofComparative Examples 1 to 3 had streaks in the warp direction,exhibiting poor appearance. In Comparative Example 4, yarns frequentlybroke during the preparation of the covered yarns. In particular, it wasdifficult to obtain a covered yarn for warp.

INDUSTRIAL APPLICABILITY

The polyurethane elastic fibers of the present invention are excellentin heat-setting properties, heat resistance, and stretching properties.Thus, the fibers, alone or in combination with other various fibers, canprovide an excellent stretch fabric and they are suitably knitted,weaved, or processed into strings.

Specific examples of the applications include fiber products such assocks, stockings, circular-knitted fabric, tricot, swimsuits, ski pants,work clothes, coveralls, golf pants, wet suits, brassieres, girdles, andgloves, constrictive materials, constrictive materials for leakageprevention for sanitary products such as paper diapers, constrictivematerials for waterproof materials, fishing lures, artificial flowers,insulating materials, wiping cloth, copier cleaners, and gaskets.

1. Polyurethane elastic fibers obtained by spinning a polyurethaneresin, the polyurethane resin comprising, as constituent units: a diol(a1) having a number average molecular weight of 500 to 10,000; anorganic diisocyanate (b); and a chain extender (a2), the totalconcentration of urethane groups and urea groups in the polyurethaneresin being 1.25 to 2.50 mmol/g based on the weight of the polyurethaneresin, hard segment domains of the polyurethane resin having an averagedomain size of 20 to 30 nm as measured with an atomic force microscope.2. The polyurethane elastic fibers according to claim 1, wherein thepolyurethane resin comprises a block (B1) and a block (B2), the block(B1) includes the diol (a1) having a number average molecular weight of500 to 10,000 and an organic diisocyanate (b1) that reacts with the diol(a1) having a number average molecular weight of 500 to 10,000, theblock (B1) has a number average molecular weight (M_(B1)) of 4,000 to80,000 as calculated by Formula (1): $\begin{matrix}{M_{B\; 1} = {\frac{{k \times M_{a\; 1}} + {r \times M_{b\; 1}}}{r - k} - {M_{b\; 1} \times 2}}} & (1)\end{matrix}$ wherein M_(a1) represents the number average molecularweight of the diol (a1) having a number average molecular weight of 500to 10,000; M_(b1) represents the number average molecular weight of theorganic diisocyanate (b1); k represents the number of moles of the diol(a1) having a number average molecular weight of 500 to 10,000; and rrepresents the number of moles of the organic diisocyanate (1)1), theblock (B2) includes the chain extender (a2) and an organic diisocyanate(b2) that reacts with the chain extender (a2), and the block (B2) has anumber average molecular weight (M_(B2)) of 1,400 to 25,000 ascalculated by Formula (2): $\begin{matrix}{M_{B\; 2} = {\frac{{i \times M_{a\; 2}} + {j \times M_{b\; 2}}}{i - j} + {M_{b\; 2} \times 2}}} & (2)\end{matrix}$ wherein M_(a2) represents the number average molecularweight of the chain extender (a2); M_(b2) represents the number averagemolecular weight of the organic diisocyanate (b2); i represents thenumber of moles of the chain extender (a2); and j represents the numberof moles of the organic diisocyanate (b2).
 3. The polyurethane elasticfibers according to claim 1, wherein the polyurethane resin satisfiesthe following requirements (1) to (3): (1) The ratio of the number ofmoles of the diol (a1) having a number average molecular weight of 500to 10,000 to the number of moles of the organic diisocyanate (1) thatreacts with the diols (a1) having a number average molecular weight of500 to 10,000 is as follows: The ratio diol (a1) having a number averagemolecular weight of 500 to 10,000:organic diisocyanate (1)1) is 1:1.05to 1:1.5; (2) The total number of moles of the organic diisocyanate(b 1) and the organic diisocyanate (b2) that reacts with the chainextender (a2) is 1.3 to 4.2 times the number of moles of the diol (a1)having an number average molecular weight of 500 to 10,000; and (3) Thetotal number of moles of the diol (a1) having a number average molecularweight of 500 to 10,000 and the chain extender (a2) is equal to thetotal number of moles of the organic diisocyanate (1) and the organicdiisocyanate (b2).
 4. The polyurethane elastic fibers according to claim1, wherein the diol (a1) having a number average molecular weight of 500to 10,000 is at least one diol selected from the group consisting ofpolyoxyethylene glycol, poly(oxy-1,2-propylene)glycol,polyoxytetramethylene glycol, a copolymer diol of tetrahydrofuran andethylene oxide, and a copolymer diol of tetrahydrofuran and3-methyltetrahydrofuran.
 5. The polyurethane elastic fibers according toclaim 1, wherein the organic diisocyanate (b) comprises a C8-C26aromatic diisocyanate.
 6. The polyurethane elastic fibers according toclaim 1, wherein the chain extender (a2) comprises alow-molecular-weight diol having a chemical formula weight or numberaverage molecular weight of less than
 500. 7. The polyurethane elasticfibers according to claim 1, wherein the polyurethane resin has a numberaverage molecular weight of 20,000 to 200,000.
 8. The polyurethaneelastic fibers according to claim 1, wherein the polyurethane resin hasa thermal softening point of 180° C. to 280° C.
 9. Polyurethane elasticfibers obtained by spinning a polyurethane resin composition thatcomprises the polyurethane resin according to claim 1 and an additive.10. A method of producing the polyurethane elastic fibers according toclaim 1, comprising: spinning by dry spinning.